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    <title>Document</title>
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    <script>
        let arr = [1, 2, 3, 4, 5, 4, 3, 2, 1];
        //1．数组去重
        // let result = [ ...new Set(arr)];
        // console.log(result);
        let arr2 = [4, 5, 6, 5, 6];
        //交集
        // let result = [...new Set(arr)].filter(item => {
        //     let s2 = new Set(arr2);// 4 5 6
        //     if (s2.has(item)) {
        //         return true;
        //     } else {
        //         return false;
        //     }
        // });
        // let result = [...new Set(arr)].filter(item => new Set(arr2).has(item));
        // console.log(result);
        //并集
        let union = [ ...new Set([ ...arr, ...arr2])];
        console.log(union);
        //补集
        let diff = [...new Set(arr)].filter(item => !(new Set(arr2).has(item)));
        console.log(diff);





    </script>
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